• Title/Summary/Keyword: Non-Quasi-Static effects

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Accurate parameter extraction method for FD-SOI MOSFETs RF small-signal model including non-quasi-static effects (NQS효과를 고려한 FD-SOI MOSFET의 고주파 소신호 모델변수 추출방법)

  • Kim, Gue-Chol
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.11 no.10
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    • pp.1910-1915
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    • 2007
  • An accurate and simple method to extract equivalent circuit parameters of fully-depleted silicon-on-insulator MOSFETs small-signal modeling operating at RF frequencies including the non-quasi static effects is presented in this article. The advantage of this method is that a unique and physically meaningful set of intrinsic equivalent circuit parameters is extracted by de-embedding procedure of extrinsic elements such as parasitic capacitances and resistances of MOSFETs from measured S-parameters using simple Z- and Y- matrices calculations. The calculated small-signal parameters using the presented extraction method give modeled Y-parameters which are in good agreement with the measured Y-parameters from 0.5 to 20GHz.

Neck Formation in Drawing Processes of Fibers

  • Chung, Kwansoo;Yoon, Hyungsop;Youn, Jae Ryoun
    • Fibers and Polymers
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    • v.2 no.1
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    • pp.140-143
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    • 2001
  • To better understand the formation of necking in drawing processes of fibers, strain distributions during drawing processes have been analyzed. For simplicity, one-dimensional incompressible steady flow at a constant temperature was assumed and quasi-static model was used. To describe mechanical properties of solid polymers, non-linear visco-plastic material properties were assumed using the power law type hardening and rate-sensitive equation. The effects of various parameters on the neck formation were matematically analyzed. As material property parameters, strain-hardening parameter, visco-elastic coefficient and strain-rate sensitivity were considered and, for process parameters, the drawing ratio and the process length were considered. It was found that rate-insensitive materials do not reach a steady flow state and the rate-sensitivity plays a key role to have a steady flow. Also, the neck formation is mainly affected by material properties, especially for the quasi-static model. If the process length changes, the strain distribution was found to be proportionally re-distributed along the process line by the factor of the total length change.

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Ratcheting analysis of joined conical cylindrical shells

  • Singh, Jaskaran;Patel, B.P.
    • Structural Engineering and Mechanics
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    • v.55 no.5
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    • pp.913-929
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    • 2015
  • The ratcheting and strain cyclic behaviour of joined conical-cylindrical shells under uniaxial strain controlled, uniaxial and multiaxial stress controlled cyclic loading are investigated in the paper. The elasto-plastic deformation of the structure is simulated using Chaboche non-linear kinematic hardening model in finite element package ANSYS 13.0. The stress-strain response near the joint of conical and cylindrical shell portions is discussed in detail. The effects of strain amplitude, mean stress, stress amplitude and temperature on ratcheting are investigated. Under strain symmetric cycling, the stress amplitude increases with the increase in imposed strain amplitude. Under imposed uniaxial/multiaxial stress cycling, ratcheting strain increases with the increasing mean/amplitude values of stress and temperature. The abrupt change in geometry at the joint results in local plastic deformation inducing large strain variations in the vicinity of the joint. The forcing frequency corresponding to peak axial ratcheting strain amplitude is significantly smaller than the frequency of first linear elastic axial vibration mode. The strains predicted from quasi static analysis are significantly smaller as compared to the peak strains from dynamic analysis.

Evaluating the accuracy of mass scaling method in non-linear quasi-static finite element analysis of RC structures

  • A. Yeganeh-Salman;M. Lezgy-Nazargah
    • Structural Engineering and Mechanics
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    • v.85 no.4
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    • pp.485-500
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    • 2023
  • The non-linear static analysis of reinforced concrete (RC) structures using the three-dimensional (3D) finite element method is a time-consuming and challenging task. Moreover, this type of analysis encounters numerical problems such as the lack of convergence of results in the stages of growth and propagation of cracks in the structure. The time integration analysis along with the mass scaling (MS) technique is usually used to overcome these limitations. Despite the use of this method in the 3D finite element analysis of RC structures, a comprehensive study has not been conducted so far to assess the effects of the MS method on the accuracy of results. This study aims to evaluate the accuracy of the MS method in the non-linear quasi-static finite element analysis of RC structures. To this aim, different types of RC structures were simulated using the finite element approach based on the implicit time integration method and the mass scaling technique. The influences of effective parameters of the MS method (i.e., the allowable values of increase in the mass of the RC structure, the relationship between the duration of the applied load and fundamental vibration period of the RC structure, and the pattern of applied loads) on the accuracy of the simulated results were investigated. The accuracy of numerical simulation results has been evaluated through comparison with existing experimental data. The results of this study show that the achievement of accurate structural responses in the implicit time integration analyses using the MS method involves the appropriate selection of the effective parameters of the MS method.

Dynamic responses of an FPSO moored on sloped seabed under the action of environmental loads

  • Roy, Shovan;Banik, Atul K.
    • Ocean Systems Engineering
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    • v.8 no.3
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    • pp.329-343
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    • 2018
  • The inclination of seabed profile (sloped seabed) is one of the known topographic features which can be observed at different seabed level in the large offshore basin. A mooring system connected between the platform and global seabed is an integral part of the floating structure which tries to keep the floating platform settled in its own position against hostile sea environment. This paper deals with an investigation of the motion responses of an FPSO platform moored on the sloped seabed under the combined action of wave, wind and current loads. A three-dimensional panel discretization method has been used to model the floating body. To introduce the connection of multi-segmented non-linear elastic catenary mooring cables with the sloped seabed, a quasi-static composite catenary model is employed. The model and analysis have been completed by using hydrodynamic diffraction code AQWA. Validation of the numerical model has been successfully carried out with an experimental work published in the latest literature. The analysis procedure in this study has been followed time domain analysis. The study involves an objective oriented investigation on platform motions, in order to identify the effects of the slopped seabed, the action of the wave, wind and current loads and the presence of riser system. In the end, an effective analysis has been performed to identify a stable mooring model in demand of reducing structural responses of the FPSO.

Non-linear vibration and stability analysis of an axially moving rotor in sub-critical transporting speed range

  • Ghayesh, Mergen H.;Ghazavi, Mohammad R.;Khadem, Siamak E.
    • Structural Engineering and Mechanics
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    • v.34 no.4
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    • pp.507-523
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    • 2010
  • Parametric and forced non-linear vibrations of an axially moving rotor both in non-resonance and near-resonance cases have been investigated analytically in this paper. The axial speed is assumed to involve a mean value along with small harmonic fluctuations. Hamilton's principle is employed for this gyroscopic system to derive three coupled non-linear equations of motion. Longitudinal inertia is neglected under the quasi-static stretch assumption and two integro-partial-differential equations are obtained. With introducing a complex variable, the equations of motion is presented in the form of a single, complex equation. The method of multiple scales is applied directly to the resulting equation and the approximate closed-form solution is obtained. Stability boundaries for the steady-state response are formulated and the frequency-response curves are drawn. A number of case studies are considered and the numerical simulations are presented to highlight the effects of system parameters on the linear and nonlinear natural frequencies, mode shapes, limit cycles and the frequency-response curves of the system.

Seismic Analysis Method for the Seismically Isolated Structures Using LRBs (적층고무베어링을 사용한 면진구조물의 지진해석방법)

  • Koo, Gyeong-Hoi;Lee, Jae-Han
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2001.10a
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    • pp.553-560
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    • 2001
  • To substantiate the application of LRB(Laminated Rubber Bearing) to the seismic isolation system, it is necessary to develop a seismic analysis method considering the non-linear behavior of LRBs, which may significantly affect the seismic responses. In this paper, seismic analyses and shaking table tests are carried out for a seismically isolated structure using four LRBs. The parameter equations of seismic isolation frequency are obtained from the shaking table tests and the quasi-static tests of LRB itself to investigate the effects of the LRB characteristics in the prediction of maximum peak acceleration responses by analysis. From the comparison of the maximum peak acceleration responses obtained from numerical analyses and experiments, it is verified that the horizontal stiffness variations of LRB should be carefully considered in seismic analysis to obtain more accurate results.

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A Modified Calculation of Electromagnetic Shielding Effectiveness Considering Some electrical Parameters (발산가응계통에서의 뉴톤-랍슨 전력게통합)

  • Sang-Jin Lee;Myung-Hwan Oh
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.31 no.12
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    • pp.173-179
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    • 1982
  • This paper presents a modified quasi-static approximate solution derived from the Maxwell's equations of integral form for the calculation of magnetic shielding effectiveness in a non-uniform enclosure such as metal-clad high-voltage test laboratory. It also describes the simplified relationship between the electrical parameters applicable to the engineering calculations of electromagnetic absorption loss which comprise the resultant effects due to the welding seams and short-circuited slots as well as the shielding material properties. A numerical example shows the fairly good agreements with experimental results measured on the absorption loss vs. incident wave frequency without any unreasonable rapid increase.

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Reduction of the residual stresses during the additive manufacturing of a thermo-viscoelastic growing cylinder under non-uniform volumetric heating by electric induction

  • Fekry, Montaser
    • Structural Engineering and Mechanics
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    • v.82 no.2
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    • pp.259-270
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    • 2022
  • The paper investigates the residual stresses arising in a thermoviscoelastic cylinder as a result of layer-by-layer deposition of material on its lateral surface. Internal stresses are caused by incompatible deformations that accumulate in the assembly as a result of joining parts with different temperatures. For the analysis of internal stresses, an analytical solution to the axisymmetric quasi-static problem of thermoelasticity for a growing cylinder is constructed. It is shown that the distribution of residual stresses depends on the scenario of the surfacing process. In this case, the supply of additional heat to the growing body can significantly reduce the unevenness of temperature fields and reduce the intensity of residual stresses. The most effective is uneven heating, which can be realized, by the action of an alternating current with a tunable excitation frequency. The temperature and residual stresses fields on the growing surface is analyzed numerically for Titanium and Copper materials.

Effects of Structured Arm Exercise on Arteriovenous Fistula Stenosis in Hemodialysis Patient (구조화된 상지운동이 혈액투석 환자의 동정맥루 협착에 미치는 효과)

  • Kim, Aee Lee
    • Journal of Korean Biological Nursing Science
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    • v.14 no.4
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    • pp.300-307
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    • 2012
  • Purpose: The purpose of this research was to develop and prove the effectiveness of structured arm exercise, which was used to reduce Arteriovenous Fistula (AVF) and Arteriovenous graft (AVG) stricture of hemodialysis patients. Methods: Quasi-experimental research design with non-equivalent control group was applied. 26 Subjects were participated in this study. 12 of hemodialysis patients who do not have a normal range of Static Intra Access Pressure Vein (SIAPV) score in the last three months were assigned to the experimental group and 14 patients who have a normal range of SIAPV score in the last three months to the control group. To analyze the collecting data after structured arm exercise, non parametric method with the repeated measures ANOVA by the Friedman test and Wilcoxon Signed Ranks Test for post-hoc test was performed. Results: Unlike the experimental group after three months, the control group's SIAPV data went over the normal range. The experimental AVF group showed a difference in data after month 2 and month 3. - In AVG group, there were clear differences in each month of the test. Conclusion: This study proved that structured arm exercise therapy could be a simple and effective intervention. It is suggested to be actively utilized for hemodialysis patients.